Dating Techniques, Stratigraphy, and Earth's Geological History

Dating Techniques and Stratigraphy

• Absolute dating provides the exact age of a rock or geological event, while relative dating orders rocks or geological events from oldest to most recent.
• An isotope refers to each of the different types of atoms of the same element, having different numbers of neutrons in their core.
• Radioactivity is used to estimate the age of rocks, and consequently, the age of the Earth.
• Half-life: The time it takes for half of a radioactive isotope to decay. Knowing the half-life allows for calculating the age of a rock by determining the proportion of the remaining radioactive element.
• Stratigraphy: The branch of geology that studies and interprets sedimentary rocks arranged in layers.
  • Taphonomy: A branch of geology that examines fossils and fossilization processes.
  • Comparative Anatomy: A discipline that studies the similarities and differences in the anatomy of organisms.
  • Biostratigraphy: A branch of geology that uses fossils to establish subdivisions of geologic time.
  • Lithostratigraphy: A branch of geology that describes geological units, attributing a specific origin.

• Principle of Superposition of Strata: States that the oldest strata occupy the basal part of a stratigraphic series.

• Index Fossil (Characteristic Fossil): An organism that lived during a specific time, evolved and disappeared suddenly, and is used to correlate different stratigraphic series.

Key Geological Events and Eras

• Orogenies: Processes of mountain and ridge formation or rejuvenation.
  • The Variscan orogeny occurred between the Devonian and Carboniferous periods, forming the Cantabrian Mountains.
  • The Alpine orogeny took place between the Mesozoic and Tertiary periods, forming the Pyrenees.
• The K-T Boundary (Cretaceous-Tertiary Boundary): A dark, sandy layer marking the end of the Mesozoic era and the beginning of the Cenozoic era. The K-T layer resulted from a meteorite impact on Earth.
• Phanerozoic Eon: Includes the Paleozoic, Mesozoic, and Cenozoic eras.
• Eon: Each of the periods into which Earth's history is divided, from a geological and paleontological perspective (eons are divided into eras).
• Young Earth formed in the Hadean Eon, and life appeared in the Archean Eon.
• During the Paleozoic Era, the continents rejoined to form the supercontinent Pangea.
• The end of the Permian Period is marked by the largest known extinction in the fossil record.
• Mesozoic Era: Characterized by the breakup of Pangea, the opening of the Atlantic Ocean (starting in the Jurassic), and the Alpine orogeny. Ammonites thrived in the sea, and reptiles, especially dinosaurs, dominated the land. A major biological extinction occurred at the end of the Mesozoic, caused by intense volcanism and a meteorite impact.
• The Betic Cordillera, Pyrenees, and the Iberian mountain range formed during this time.
• During the Quaternary Period, humans appeared on Earth, and intense glaciations occurred.